The present invention relates to toxins isolated from bacteria and the use of said toxins as insecticides.
Many insects are widely regarded as pests to homeowners, to picnickers, to gardeners, and to farmers and others whose investments in agricultural products are often destroyed or diminished as a result of insect damage to field crops. Particularly in areas where the growing season is short, significant insect damage can mean the loss of all profits to growers and a dramatic decrease in crop yield. Scarce supply of particular agricultural products invariably results in higher costs to food processors and, then, to the ultimate consumers of food plants and products derived from those plants.
Preventing insect damage to crops and flowers and eliminating the nuisance of insect pests have typically relied on strong organic pesticides and insecticides with broad toxicities. These synthetic products have come under attack by the general population as being too harsh on the environment and on those exposed to such agents. Similarly in non-agricultural settings, homeowners would be satisfied to have insects avoid their homes or outdoor meals without needing to kill the insects.
The extensive use of chemical insecticides has raised environmental and health concerns for farmers, companies that produce the insecticides, government agencies, public interest groups, and the public in general. The development of less intrusive pest management strategies has been spurred along both by societal concern for the environment and by the development of biological tools which exploit mechanisms of insect management. Biological control agents present a promising alternative to chemical insecticides.
Organisms at every evolutionary development level have devised means to enhance their own success and survival. The use of biological molecules as tools of defense and aggression is known throughout the animal and plant kingdoms. In addition, the relatively new tools of the genetic engineer allow modifications to biological insecticides to accomplish particular solutions to particular problems.
One such agent, Bacillus thuringiensis (Bt), is an effective insecticidal agent, and is widely commercially used as such. In fact, the insecticidal agent of the Bt bacterium is a protein which has such limited toxicity, it can be used on human food crops on the day of harvest. To non-targeted organisms, the Bt toxin is a digestible non-toxic protein.
Another known class of biological insect control agents are certain genera of nematodes known to be vectors of transmission for insect-killing bacterial symbionts. Nematodes containing insecticidal bacteria invade insect larvae. The bacteria then kill the larvae. The nematodes reproduce in the larval cadaver. The nematode progeny then eat the cadaver from within. The bacteria-containing nematode progeny thus produced can then invade additional larvae.
In the past, insecticidal nematodes in the Steinernema and Heterorhabditis genera were used as insect control agents. Apparently, each genus of nematode hosts a particular species of bacterium. In nematodes of the Heterorhabditis genus, the symbiotic bacterium is Photorhabdus luminescens. 
Although these nematodes are effective insect control agents, it is presently difficult, expensive, and inefficient to produce, maintain, and distribute nematodes for insect control.
It has been known in the art that one may isolate an insecticidal toxin from Photorhabdus luminescens that has activity only when injected into Lepidopteran and Coleopteran insect larvae. This has made it impossible to effectively exploit the insecticidal properties of the nematode or its bacterial symbiont. What would be useful would be a more practical, less labor-intensive wide-area delivery method of an insecticidal toxin which would retain its biological properties after delivery. It would be quite desirous to discover toxins with oral activity produced by the genus Photorhabdus. The isolation and use of these toxins are desirous due to efficacious reasons. Until applicants"" discoveries, these toxins had not been isolated or characterized.
The native toxins are protein complexes that are produced and secreted by growing bacteria cells of the genus Photorhabdus, of interest are the proteins produced by the species Photorhabdus luminescens. The protein complexes, with a molecular size of approximately 1,000 kDa, can be separated by SDS-PAGE gel analysis into numerous component proteins. The toxins contain no hemolysin, lipase, type C phospholipase, or nuclease activities. The toxins exhibit significant toxicity upon exposure administration to a number of insects.
The present invention provides an easily administered insecticidal protein as well as the expression of toxin in a heterologous system.
The present invention also provides a method for delivering insecticidal toxins that are functional active and effective against many orders of insects.